1. Field of the Invention
The present invention relates generally the projection of visible lines onto surfaces upon which persons may be standing (e.g., athletic fields during sporting or entertainment events) and, more particularly, to systems employing laser light beam sources to generate such visible lines.
2. Description of the Related Art
In the game of football, a key objective of the team in possession of the ball (i.e., the “offense”) is to retain possession of that ball by moving it far enough down the field. Specifically, the offense is given a set of four plays or “downs” to advance the ball by at least ten yards. Each time that distance is reached or exceeded, the offense is said to have crossed a “first down” line, a new set of downs is earned, and the offense is allowed to continue its advance toward the goal line of the opposing team (i.e., the “defense”). If the offense falls short, however, possession is lost and the two teams reverse their roles. A regulation football field has a length of 100 yards and 53 yards. Thus, by way of example, a team gaining possession of the ball at its own 20 yard line must move the ball a total of eighty yards in order to reach the end zone of the opposing team.
In numerous occasions throughout an average football game, the officials of the game must resort to sideline markers to establish whether the offense has advanced the ball by the required distance. The standard alignment system that is utilized is generally a pair of poles connected by a 30 foot long chain. The relative position of the football is measured by locating a first of these poles at the approximate location of the initial line of scrimmage and moving the second as far forward as possible. Each time this measurement is made, the game must be delayed and the yard markers must be carried from the sidelines to the place on the field where the official has “spotted” the ball. Although the game of football has become a relatively complex sport, involving literally hundreds of millions of invested dollars, this time consuming system has remained relatively the same since the conception of the sport.
A number of approaches intended to ameliorate the aforementioned deficiencies have been proposed over the years. Examples of such approaches are set forth in U.S. Pat. No. 3,741,662, entitled “VISIBLE LINE MARKER” and issued to Pioch on Jun. 26, 1973, in U.S. Pat. No. 3,752,588, entitled “LASER FOOTBALL FIRST DOWN MEASURING DEVICE” and issued to Chapman on Aug. 14, 1973, and in U.S. Pat. No. 4,090,708 entitled “APPARATUS FOR MARKING FOOTBALL FIELDS” and issued to McPeak on May 23, 1978. Each of the aforementioned approaches involve the use of lasers for the purpose of marking visible lines of demarcation on an athletic field. One of the principal drawbacks of these systems is the time-consuming and tedious method of operation.
Both Chapman and Pioch involve the use of track mounted, sliding projectors that are located at the sidelines and several feet above the field level. The lasers are mounted for oscillation in a vertical plane and the projected, low intensity beam developed by each must strike the field at points of reference lying on an imaginary line of demarcation defined by the intersection of the vertical plane with the field surface. Like Pioch and Chapman, McPeak discloses the use of laser assemblies adapted to accommodate sliding movement along the sidelines of a football field. Peak, however, teaches that two oppositely directed beams should be aimed at a level above (i.e., “adjacent and parallel to”) the field surface. A key drawback associated with the aforementioned systems is that the low-intensity output of the lasers used is far too low to be visible by the players in ambient daylight conditions, let alone by spectators in a stadium.
Television networks have recently implemented an image pre-processing system which allows viewers of televised football games to see a so-called “virtual” first down line that digitally projects, in real time, a visible line onto video frames recorded by the television camera, the line being displayed on a viewer's television set so that it appears to extend between the first down sideline markers. Unfortunately, neither the players, game officials, nor the fans attending such games can actually see this virtual line.
The inventor herein has previously proposed several different systems and methods for projecting a visible reference light onto an athletic field. These systems are described in U.S. Pat. No. 7,219,438 filed on May 3, 2004 and entitled “SYSTEM FOR OPERATING ONE OR MORE LASERS TO PROJECT A VISIBLE LINE ONTO A SURFACE”, U.S. Pat. No. 6,796,041 filed on Mar. 10, 2003 and entitled “SYSTEM FOR OPERATING ONE OR MORE SYNCHRONIZED LASERS TO PROJECT A VISIBLE LINE ONTO A SURFACE”, and U.S. Pat. No. 6,751,880 filed on Mar. 10, 2003 and entitled “SYSTEM AND METHOD FOR OPERATING GROUPS OF LASERS TO PROJECT A VISIBLE LINE OF DEMARCATION ONTO DISCRETE REGIONS OF AN ATHLETIC FIELD”, as well as U.S. patent application Ser. No. 10/320,304 filed on Dec. 16, 2002 and entitled “SYSTEM AND METHOD FOR DYNAMICALLY MARKING ATHLETIC FIELDS USING A HANDHELD USER INTERFACE”, all of which are expressly incorporated herein by reference in their entirety.
The aforementioned laser projection systems, while functional for the intended purpose, require customized installation and are somewhat complex and expensive to operate and maintain. A continuing need exists therefore exists for a system which is capable not only of projecting a line which can be seen from different perspectives and from considerable distances—even in daylight condition, but also of doing so in a manner that is safe, relatively simple and inexpensive to install and maintain.
A need also exists for a system that is capable of projecting a line which, though intense enough to be seen from a wide range of viewing angles, conforms to all applicable eye-safety regulations such as those promulgated by the FDA's Center for Diagnostic and Radiological Health (CDRH).